Neodymium-yttrium-argon laser

Before the invention of lasers in 1960 (Maiman), radiation emitted by the mercury arc, especially at 435.8 and 404.7 nm, has been u.sed for exciting Raman spectra (Brandmiiller and Moser, 1962). Today, most types of lasers ( continuous wave (cw) and pulsed, gas, solid state, semiconductor, etc.), with emission lines from the UV to the NIR region, are used as radiation sources for the excitation of Raman spectra. Especially argon ion lasers with lines at 488 and 515 nm are presently employed. NIR Raman spectra are excited mainly with a neodymium doped yttrium-aluminum garnet laser (Nd YAG), emitting at 1064 nm. 

Laser Ablation [7]. The modern method for quantitative solid analyses is carried out using a laser ablation technique (Figure 2.16). The laser, usually in the form of Nd YAG (Neodymium - Doped Yttrium Aluminium Garnet), is focused on to the surface of a sample which, by continuous pulsing, leads to vaporisation at that point and the vapour is transported directly to the plasma with argon for detection and quantification. Detection limits are... 

Many real-world samples fluoresce when iUuminated with visible light, especially green light from a frequency-doubled neodymium-doped yttrium aluminum garnet (Nd-YAG) laser at 532nm or from an argon ion laser at 488 or 514.5nm. 

Thus, a high frequency excitation source enhances the number of scattered Raman photons dramatically. As an example, let us consider the relative intensity of a 1000 cm Raman line excited at 1064 nm and also excited at 514 nm. The first wavelength is available from an Nd YAG (yttrium aluminum garnet doped with neodymium) diode laser, and the second from an argon ion laser. Using the excitation at 1064 nm the 1000 cm Raman band occurs at 1191 nm, and for the excitation at 514 nm the Raman line would occur at 542 nm. Therefore, the enhancement of the 514 nm excitation relative to the 1064 nm excitation would be by a factor (1191/542)" = 23.3. This means that there are 23.3 times as many photons to detect with the shorter wavelength excitation simply as a consequence of the nature of the scattering process. This can be a very important effect. 

Laser is an acronym for light amplification by simulated emission of radiation. In SERS, as well as in other types of Raman scattering experiments, a continuous-wave (CW) gaseous ion laser is normally used, e.g., an argon-or krypton-ion laser. It is also possible to use a pulsed laser, such as a neodymium, Nd ", in yttrium-aluminum garnet (YAG) laser however, a much... 

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